Advances in nanoporous membrane design with improvements in chemical selectivity and high flux may directly benefit a number of fields, including chemical separations, ion channel mimetics, drug delivery, and wastewater remediation. Matching pore size of such membranes to target molecule size is important in that it allows molecular sieving and forces interactions with chemically selective molecules associated with the membrane pore. This is a particularly difficult challenge in the nanometer pore size range.
Various approaches have been investigated, including inorganic materials such as inorganic porous ceramic membranes, silica, alumina, zirconia, zeolite, and carbon. Inorganic membranes are very robust, and do not suffer from solvent effects. However, high surface area inorganic membranes are expensive and mechanically fragile. Organic membranes are most prevalent, but suffer from difficulty in regulating pore size, and also from solvent effects (swelling) which alter pore size, affecting selectivity and throughput. Exemplary organic membranes studied include functionalized polymer affinity membranes, block copolymers, and mesoporous macromolecular architectures.
Nanometer-scale control of pore geometry and demonstration of molecular separations have been achieved also through the plating of nanoporous polycarbonate ion track-etch and ordered alumina membranes with initial pore dimensions of approximately 20 to 50 nm. A major challenge to improving selectivities of pore-plated membranes is minimizing the variations in initial alumina pore diameters, because the resultant diameter is the difference between the plating thickness and the initial pore diameter. It is accordingly desirable to begin with a membrane structure having an initial pore diameter near that of the target molecule(s), with limited dispersion.
It is also desirable for such nanoporous membranes to be reversibly gated, to mimic natural biological systems such as for example the nicotinic acetylcholine receptor, which is one of the most widely studied ligand-gated ion channels. In this field, organic membranes such as aromatic/polycarbonate copolymers, cellulose acetate, aliphatic polyamides, polyimides, polydimethylsiloxone, and polysulfone have been studied. In particular, polysulfone membranes have been evaluated for use as affinity membranes. Hydrogels have also been studied for use as gated membranes due to their reversible phase change, which is mostly controlled by external chemical stimuli such as pH, temperature, or variation in electric charge. However, molecular diffusivity is low in hydrogels because of restricted chain mobility. Further, volume changes in hydrogel require a lag time, and hydrogel membranes lack mechanical stability.
The present invention addresses the identified need in the art by providing a method for fabricating a nanoporous ordered membrane, and a membrane fabricated thereby. Advantageously, the membrane of the present invention is stable and provides a tightly controlled pore size, and is resistant to solvent effects. Still further, the membrane of the present invention can be functionalized in a variety of ways at the pore openings to impart selectivity to the membrane, to provide a selectively gateable membrane as well as other functions.